Benzoyl isothiocyanate as a precursor to design of ultrathin and high-crystalline g-C3N4-based donor–acceptor conjugated copolymers for superior photocatalytic H2 production

Abstract

Graphitic carbon nitride (g-C3N4) has been demonstrated as ideal photocatalyst for photocatalytic H2 evolution, but simultaneously improves the photocatalytic activity and the apparent quantum efficiency (AQE) remains a big challenge. Recently, ultrathin and donor–acceptor (D-A) conjugated structure have attracted considerable attention in photocatalytic H2 evolution, which are capable to favorable provide more reactive sites and forward intramolecular charge separation. Inspired by these advantages, benzoyl isothiocyanate (BI) as a precursor is used to design the ultrathin g-C3N4 (UCN)-BIx D-A conjugated copolymers by copolymerization with urea, which can favor forward intramolecular charge separation so as to achieve ultrahigh photocatalytic activity and AQE in photocatalytic H2 evolution. The experimental results and density functional theory (DFT) calculations reveal that the obtained UCN-BIx D-A conjugated copolymers not only represent effective suppression of charge reverses recombination and but also broaden the range of light absorption. Additionally, UCN-BIx D-A conjugated copolymers has higher crystallinity and more negative conduction band (CB) position relative to the pure g-C3N4. And femtosecond transient absorption (fs-TA) spectroscopy also indicates that UCN-BI400 D-A conjugated copolymer shows the forward transfer ability of charge carriers is enhanced effectively. Marvelously, the best photocatalytic H2 evolution activity over UCN-BI400 D-A conjugated copolymer (5442.74 μmol g-1h−1) has driven by visible light exhibits an 11.96-fold enhancement relative to pure g-C3N4. Most noteworthy, the AQE of 23.7% and 7.0% is achieved at 420 nm and 450 nm that far exceeds majority of the previously reported g-C3N4-based D-A conjugated structures and UCN nanosheets. This contribution extends a novel design concept of effectively combining the ultrathin and D-A conjugated structures to simultaneously improving the activity and AQE of photocatalytic H2 production.